Moving Air

Let’s Talk About It

As a class, discuss students’ predictions about the effects of warm and cool air on their bubbles. Then talk about what actually happened.

Tell students that temperature determines how much the molecules in air move and how much space air can take up. Ask students, Why did the bubble film dip below the top of the can when you placed the can in ice water? Be sure that the students understand the ice water cooled the molecules in the air, which caused the molecules to move less and push less against each other and the sides of the container than they did in warmer air.

Continue the discussion by asking students to explain what happened to the bubble film when the can was placed in the warm water. In this case, students should understand that when the molecules in the air were warmed by the water, they moved more and bounced more against each other and against the bubble top of the container than they did when the air was cooler.

Next, ask students, What do you think will happen if we heat the air in the can even more? As a class demonstration, dip the open end of another can in bubble solution, and then heat the bottom of the can using a lighted candle or hotplate. The bubble will bulge much more dramatically than when the can was placed in warm water.

Extend students’ discoveries about the movement of air by encouraging students to think about what might be happening with the air inside the classroom right now. Ask, What happened to the air inside the can when it was placed in cold water? In warm water?

Begin a general class discussion by asking, Is all the air in this room the same temperature? If not, what are the sources of different temperatures of air? What will happen if the air in one part of the room is warmer than air in another part of the room?